The book begins with a historical introduction, Star Formation: The Early History , that presents new material of interest for students and historians of science. This is followed by two long articles on Pre-Main-Sequence Evolution of Stars and Young Clusters and Observations of Young Stellar Objects . These articles on the fascinating problem of star formation from interstellar matter give a thorough overview of present-day theories and observations. The articles contain material so far unpublished in the astronomical literature. The book addresses graduate students and can be used as a textbook for advanced courses in stellar astrophysics.